1. Field of the Invention
This invention relates to an improvement in the mechanism for igniting a gas generator or inflator of the type that utilizes the combustion of a solid fuel gas generant composition for the generation of a gas to inflate an inflatable crash protection air bag or cushion. The invention is particularly advantageous for use in a gas generator provided on the passenger side of an automotive vehicle.
2. Description of the Related Art
Typically, a solid fuel gas generator for the passenger side of an automotive vehicle is elongated. In one embodiment, the gas generator has a length of 11.82 inches (30.02 cm) and an overall diameter of 2.43 inches (6.17 cm). An elongated tubular outer housing for the generator advantageously may be made of aluminum. For most of the length thereof, the outer housing has a relatively thin cylindrical wall in which a plurality of gas exit holes or ports are provided.
One end of the outer housing, termed the stud end, is closed by material formed integrally therewith and includes a threaded stud projecting therefrom. The other end of the outer housing, termed the base end, is closed by a flange. The flange member is attached in a sealing manner to the base end of the outer housing by a suitable process such as inertia welding. A welding process that may be employed is described in U.S. Pat. No. 4,547,942 to Adams et al., which patent is assigned to the assignee of the present invention and the disclosure of which, by reference, is incorporated herein. The flange member serves as a squib and initiator holder.
Extending for a substantial portion of the length of the outer housing and centrally thereof so as to be generally concentric therewith, is an elongated generally cylindrical tubular member comprising an igniter tube. The igniter tube contains ignition granules of an appropriate pyrotechnic material capable of providing rapid deflagration. A squib and initiator are provided in operative relation with and close to the end of the igniter tube that is adjacent to the base end of the housing. At the stud end of the housing the igniter tube is closed by a rubber boot. The rubber boot incorporates an ignition granule retention disk.
A tube locator cap comprising a silicone pad is positioned adjacent to the inner side of the integrally formed end at the stud end of the housing and a retaining cup is positioned adjacent the inner side of the base end of the housing for facilitating positioning of the igniter tube and for retaining it in place. A retainer disk is provided to keep the retaining cup and the gas generant material in place within the housing during the assembly operation, suitably spaced from the flange member which spins relatively to the base end of the housing during the inertia welding operation.
Also extending over a substantial portion of the length of the tubular housing and positioned concentrically therein is an elongated perforated cylindrical inner tube or basket. The inner tube is positioned concentrically relatively to the igniter tube and outer housing by means of a circular groove in a silicone pad at the stud end of the housing and by a silicone pad positioned against the retainer disk adjacent to the flange member at the base end of the housing.
Gas generant material is contained in an elongated space or region having an annular cross section between the igniter tube and the inner tube or basket. The annular space is the combustion or gas generant chamber of the gas generator.
Upon initiation of gas generation, generated gases flow from the combustion chamber through perforations in the perforated inner tube into a radially outward space or region having an annular cross section located between the inner tube and the inner wall of the housing. A gas filtering assembly is positioned in this radially outward positioned space. Positioned between the filtering assembly and the wall of the housing is a foil seal barrier.
In the operation of a gas generator as described herein, several problems have been encountered involving post fire flammable outgassing. This is the result of non-pyrotechnic flammables from inside the gas generator. In addition the rubber boot on the end of the igniter tube is susceptible to being pulled off or forced over the igniter tube during installation or assembly anomalies. Such displacement of the rubber boot tends to result in loss of ignition granules from the igniter tube which can cause ignition irregularities.
Thus, there is a need and a demand for an improved igniter system for the passenger air bag gas generator that provides a positive retention system for the ignition granules in the igniter and will withstand installation anomalies and last for the lifetime of environments experienced by the gas generator assembly.